Most of us think very little about fungi. When we do, we usually think of mushrooms. But mushrooms are only the small parts of fungi that help them reproduce. Most fungus is in the soil in the form of thousands of fine filaments. It was widely reported some time ago that fungi might include some the largest living organisms on earth. What appeared to be single individual fungus was found in Oregon covering 2200 acres of forest floor. In fact, this cannot be proved because you would have to dig the whole thing up to see if it was connected and it most likely consists of many clones. Nevertheless, the soil is riddled with tons of fungal filaments.
Some of these filaments perform a number of critical functions in the lives of plants.
There are many species of fungi that attach themselves to the roots of specific plants. Some of these form tiny capsules on the tips of roots and others grow right into the roots. Both types extend the reach of these roots far out into the soil. This is a relationship in which both the plant and the fungus benefit. Just like in Star Trek, they are symbionts. The fungus gets some of the sugars that the plant creates in its leaves and the plant gets some of the water and nutrients that the fungus is able to obtain from soil. These fungi are able to extract some nutrients from the soil better than plants and they share them. The Peterborough Master Gardeners attended a workshop last weekend at the Ecology Park to learn more about trees from Cathy Dueck. She explained to us that some of the native trees that Ecology Park was growing in pots were not thriving. They took some of the soil from under a full-grown tree of the same species and added it to the pots and the trees began to flourish. Clearly, the small trees needed their symbionts.
This is not even the most important service performed by fungi for plants.
The fungal threads in the soil are relatively short lived and are constantly being replaced, as are the root hairs of plants. About 10 years ago it was discovered that these filaments are coated with a sticky substance. The fungus uses this substance called glomalin to keep the water and nutrients from leaking out into the surrounding soil and to stiffen their filaments. As the threads disintegrate they leave behind this substance which causes the soil particles to stick together in clumps. Clumping of soil particles gives soil its structure, holding water and nutrients and creating air spaces critical for the survival of plants. A significant amount of the earth's carbon is also stored in glomalin.
The fungal filaments are not necessarily present in sterilized growing media or in soil where there is insufficient organic matter for them to grow. They also can be disrupted by the plowing of fields and digging in gardens. Healthy undisturbed soil, rich in organic matter encourages these helpful fungi.
Some of you may have a sandy soil. Some of you may have a clay soil. And some of you may have the perfect loam that all gardeners crave. But if you do not have enough organic matter, any type of soil compacts deteriorates and erodes. This is partly because a soil poor in organic matter is inhospitable to soil organisms including fungi. Fungi play a crucial role in transferring the goodness from this organic matter to your plants.
What does all this mean for gardeners? Almost any soil problem you might have can be remedied by adding finished compost like the compost you can get from the City of Peterborough. If you just leave it on the top of your garden you will suppress the weeds and the worms will do the work of taking it down. Fertilizing your plants or your lawn with chemicals does not always encourage the processes that create a healthy resilient soil structure. Every year I find more evidence that if you look after your soil and everything living in it including fungi, then the soil will look after your plants. So next time you see a mushroom in your lawn remind yourself that things must be working underground.